To establish the effect of long-term treatment with raloxifene, compared with placebo, on the rate of new vertebral fractures in osteoporotic post- menopausal women with and without prevalent vertebral fractures. To establish the safety of chronic administration of raloxifene in post- menopausal women with osteoporosis. To establish the effect of long-term treatment with raloxifene, compared with placebo, on lumbar spine and femoral neck bone mineral density (BMD) in postmenopausal women with osteoporosis.